Britannia 70047 "Derek Stokes"

[JonL]

Cashflow stops play a little, so I'm working on what I have without needing to get new components or materials. I've made the upper guide bars today,machining them from a larger piece of metal so they are as square as I can make them. next up I need to make the lower guide bars, the rod is on the way.

If I run out of things to do I may start on the smokebox as I have all the materials for that. Onwards and upwards!

[JonL]

I've started to make the guide bars now. all the holes have been drilled, threads tapped and dimensions internally to size. The outside profile is almost right, but I've deliberately left it slightly oversize so I can make the edges blend together once assembled. The 7BA bolts required are in the post.

[JonL]

I've been trying to grip the cast slide bar brackets in the clamp for the vertical slide tonight but it kept slipping, at one point causing a gouge in one of my castings. I've decided to shut the door on the workshop and walk away quietly for the evening... I'll have another go tomorrow.

[Deleted]

Bet you it goes smoothly tomorrow, good luck..

[JonL]

Thank you. I think I just need to work out a better method for holding them. It's quite a complicated shape casting and I was having cold sweats about clamping something too hard and cracking a casting. I was trying to choose places to clamp with webs and such to clamp on rather than open space between the parts I'm gripping. I've got a swivling vertical slide that I've never used before (It needed all the protective wax removing from the slides before it would even move! Still in 40 year old waxed paper), however its using the same clamp as I use on my non-swivling vertical slide. I'll try some alternative techniques tonight. Not going to be beaten!

[Deleted]

Hi Nobby, I don't envy you doing everything with the lathe, that's a lot of extra checking. Interestingly, Don's words for 'Doncaster' are all on the lathe, I believe that he didn't own a mill (Julian?). He got his friend and very experienced/known model engineer to machine the cylinders and insisted that he (Mervyn (spelling?), better known as Merlin I believe) did everything on the lathe to prove that it can be done. BTW, Merlin destroyed his first attempt at machining the middle cylinder, even the experts make mistakes...
Going back to your setup, I wouldn't personally change to the swivel type, to me that's just adding another possible problem in ensuring it's square. It's worth taking a lot of time in setting up, when I first worked on my cylinder it probably took me a day or two making up the various jigs to hold the casting both securely and in it's correct positions as I have a 7 degree incline between the main bore and the steam chest, so needed two support blocks, all good fun though..... yeh right...

Pete

[JonL]

I've got both types; I decided to try the swivelling type as I thought I might be able to pick the best place to grip the casting and then align it afterwards. I think my main issue is with physical grip. I just can't seem to grip the component in my clamp without it moving in the jaws.

Thanks for all the tips, I'm grateful and learning.

[Deleted]

Can you share a picture if your setup, perhaps some may be able to make suggestions to help?

[JonL]

Good idea, I'll take some tonight. The main issue is I don't want to crack a casting by tightening it up on a weak spot!

[franstrein]

Hi Nobby,

I tackled that problem by, after initial cleansing, first clamping it in a vice, and milling the face plus mounting holes, using my CNC mill:


Result is:


That was followed by mounting both left and right pieces onto a square mounting block, with the appropriate holes, which I could then clamp on my mill, for subsequent processing:





The final result, with the mounted slide bars and cross-head:



Let me know in case you need more info,
Frans

P.S. Last month I had the first run of my Brit on compressed air, running on the first, left, cylinder only on the workbench:
See Test run of my Brit

[JonL]

That looks fantastic, well done Frans. I can't view the video where I am at the moment but be sure I will very soon.

[JonL]

This is the pesky casting I'm trying to hold. I managed to do so once I'd made some packing pieces to go between the webs so I could clamp one face.




First check and all seems good. Not sure I'll do much to the casting between the webs other than basic tidying, seems like a hiding to nothing. Lots more to do, and its taken quite a long time to get this far, with another side still to do.

[Deleted]

Looks like you have machined some of the faces. If it was me with the limited options using a vertical slide I'd make a simple jig. I can see from Frans's photos the various holes for bolting to frames and slide bars, I would make use of these. Get one face machined, plot and drill the holes for that face and use these to bolt the casting to a suitable piece of steel that can be held securely in the vertical slide. If you plan it out so that you can reach all sides of the casting when fitted to the jig (piece of steel bar) it could be used for all other machining operations. You may need some packing for some operations for extra rigidity as you don't want to rely on the mounting bolts alone. All set ups are a matter of trial and error in one form or another...

[JonL]

I found once I had a couple of the sides machined I had a positive surface to grip on without too much fear, so after a bit of bumbling around trying and failing to find suitable fasteners to mount this to a plate I got impatient and cracked on with it.

For some reason the goddess of shonky machinists decided to let me get away with it, just this once, and I've managed to machine most of the other faces just fine. I forgot to take a photo before I slapped a layer of paint on (I wanted to see if the faint circles caused by the tool would show through paint) so all I have is this of the almost finished object.




It's not there yet but I'm happy with how its coming together, the dimensions are right anyway. That picture makes the finish look dreadful but actually its beautifully smooth in the flesh. What I haven't done in the lathe I've done by hand with a file. Filing is probably my favourite part of finishing components. Funny, on my apprenticeship I hated it!


Please don't feel I'm ignoring the advice I'm being given, I just don't have the big come-in-handy-box that most people have (I was impatient this time, should have purchased the additional parts needed but didn't, and for some reason I didn't pay dearly for my rash choices). My workshop is barely a few months old, so I don't have much scrap metal, or spare fasteners, or anything really. Whenever I make anything 9 times out of 10 I have to buy every single bit of raw stock, every fastener, and often additional tools. Taps and Dies especially are a pain, I feel my heart sink every time LBSC mentions a new one as you can bet your bottom dollar its one I don't have! Sometimes I've used close approximations without issue, other times its get back on to Proops or similar and get the next taps and dies ordered.

Anyway, what I'm trying to say is, advice is very welcomed (thank you, I appreciate it), and I'll do my best to follow it especially when its as useful as the pieces I've been given so far, but a lot of the time I lack the scrap metal to make additional packing pieces, clamps and mounts.

[David]

Looks good Nobby, not sure what rough looking finish you're referring to.

I'm lucky in that I can borrow the less frequently used taps and dies like those over 3/8 inch but I am in the same boat when it comes to material. I have some round bar and a few pieces of thin steel a sheet of brass, but bigger pieces of steel and aluminium such as I'd like for fixtures are not in evidence in my workshop.

[dhamblin]

Nothing wrong with that at all, also means you stand a good chance of getting the second bracket right as well.

A little tip - I found out that an electric toothbrush and paraffin is really good at getting congealed oil and track rust out from between those gussets on it.

Regards,

Dan

[uuu]

But you have to rinse it thoroughly afterwards, or it tastes dreadful.

[JonL]

I'll use my girlfriends then.

[JonL]

Trial assembly of the right hand crosshead. I had two choices for my crosshead, a pair that SimplyLoco kindly donated to the cause, and some castings that came in the job-lot I bought at the start of this build. I decided to use the excellently engineered SimplyLoco (TM) pair as a back up and have a crack at the castings. I figure its a complex bit of design to do on the vertical slide, but thats where the fun is. Having John's pair sat there as backup took some of the stress out of machining the castings! As you can see from the picture they are no-where near complete, but the critical dimensions for the guide bar channels are done and work perfectly. I haven't case hardened the guide bars, it's been mentioned to me that perhaps I should. That does make me nervous about distortion however. The screws holding the guide bars probably won't hang around; they will most likely be replaced with hex heads.

Quite a rewarding couple of hours(!) in the workshop. 

[don9f]

Hi, if you case harden the guidebars (I call them slidebars), I agree that there is a risk of distortion. I made mine from gaugeplate left in its natural state and maybe you could do the same, but retain your existing spacers which would preserve the good fit you already have in the channels. For info, my crossheads are mild steel and whether or not it’s a good choice, working against gaugeplate, they show no wear after several years running.

On the other hand, if your cross heads are brass or gunmetal (as they look like in the photo), then mild steel slidebars will probably work ok!

Cheers Don